Cam and crank sensors.

[emsvitil]

You have an engine with both a cam and crank sensors.

Once you've started the engine, does the ECU even need or use the cam sensor any more?

I don't think it does once the engine is running........

[dannobee]

Nope. Way back when with the GM Buick V6 the cam sensor magnets had a habit of falling off with the engine running. The customer's complaint was that the engine was running fine, then the check engine light came on, it drove fine all the way home, then it wouldn't restart on the next try.

[rebelrouser]

I think it depends on what engine and ECM you have. Dannobee is correct on the old GM's, but any of the newer stuff especially with variable valve timing have to see a cam sensor and many have more than one cam sensor. Also newer engines all will set codes for cam crank alignment, so the ECM is always looking at cam sensors. Some of the older batch fired injection systems did not use a cam sensor. And I think for just running the engine and not trying to meet emissions a batch fired system will work just fine.

[dannobee]

With any kind of modern COP or DIS it still needs to see a cam sensor signal, otherwise the PCM won't know if the TDC is on power or overlap stroke. The newer pcm's will recognize no cam signal while cranking and try one of two ways until the rpm jumps, indicating engine start.

Agree with batch firing, although sequential engines idle smoother than the old batch fired ones.

The old engines would set codes for cam sensors too. It's just that after shutting down, the ECM forgot which stroke it was on. IE, it was only needed on initial start-up.

[Racer71]

The cam sensor is used for injector synchronization and misfire detection. Yea they will run without it but in batch fire for the injectors and no ability to detect misfires. Variable valve timing engines use them to monitor cam timing advance/retard continuously

[naukkis79]

Yeah, if cam timing is solid ECU doesn't need cam signal in running condition.

However modern ecus track both crank and cam signal all the time and have fail programs if either one of them fails. So malfunctioning crank sensor won't stall engine with modern ecus anymore.

[dannobee]

It'll still detect misfires with a failed cam sensor, but the PCM might not (reliably) know which exact cylinder is misfiring, so a generic "P0300" code will set instead of the more specific "P0301-P0308" code. The PCM looks for a decrease in crankshaft speed to determine if there's a misfire. Or more correctly, that one cylinder didn't add to the rotational speed as it should have.

[gunt]

aftermarket or oe

all the guys here run only a crank sensor in rally engines despite it requiring a cam for injection , once they were told how to format the ecu to run with out one for trouble shooting , they gave up on it , but there is a huge difference in end results , even to count fuel efficiency in racing , not something all care about , but keep it and use it

[gruntguru]

Cam sensor is also required for ignition if the system has one coil per plug. To start and run without the cam sensor such a system would need to switch to a waste-spark mode.